1. Field of the Invention
The present invention relates to the preparation of "cold-cast" flexible polyurethane foams by expansion in molds, the foaming compositions containing very small amounts of organosilicon stabilizers selected from among the triorganosilylated polypentaerythritols. The resultant foams have good physical properties, in particular high elasticity.
2. Description of the Prior Art
The so-called "cold-cast" flexible polyurethane foams, i.e., foams which do not require subsequent heating, after removal from the mold, to complete the crosslinking or curing thereof, have been manufactured and used for several years. To prepare such foams, it is essential to employ, in addition to modified or unmodified polyisocyanates, foaming agents, catalysts and stabilizers, polyether-polyols which contain at least 10%, numerically, of primary hydroxyl radicals.
These polyether-polyols are used together with organosilicon compound stabilizers having a structure markedly different from that of the polysiloxane-polyoxyalkylene block copolymers which are used for the preparation of foams requiring a heat after-treatment.
Thus, these organosilicon compounds can be triorganosilylated polyols prepared by the reaction of low molecular weight polyols, such as trimethylolpropane or pentaerythritol, with triorganohalogenosilanes such as trimethylchlorosilane or dimethylvinylchlorosilane (French Patent No. 2,288,754); such triorganosilylated polyols are used in amounts of 0.05% to 3% by weight relative to the polyether-polyols.
Other organosilicon compounds, having a slightly different structure, are also employed in amounts on the same order (compare U.S. Pat. Nos. 2,935,133, 4,016,163 and 4,067,828, French Patent No. 2,291,995 and Published European Patent Application No. 761).
Although these amounts are rather low, the manufacturers of foams have constantly strived to reduce them even further because of the relatively high price of the organosilicon compounds vis-a-vis the other constituents of the foams.